A new study suggests that the warming power of atmospheric carbon may be more …

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As most of us who follow climate research know, the forces for change in the global climate are difficult to quantify, as they are subject to both positive and negative feedbacks. Ultimately, however, it is extremely important to understand the consequences of all the extra carbon that now resides in our atmosphere. One simple value that provides a handle on this situation is what's termed the "climate sensitivity", which registers what would happen if all other variables were the same and atmospheric carbon dioxide were doubled. Observations of past warming events had suggested the the climate sensitivity might be above 7°C, which would suggest we're in for potentially catastrophic warming. A new study in Nature suggests things might not be so bad.

The study took advantage of extensive climate records in the Northern Hemisphere, and calibrated them relative to ice core and tree ring data for the last 1,000 years. They then ran over 1,000 simulations for that period, varying many of the major parameters to determine which values the climate appeared to be the most sensitive to. The two that stood out were climate sensitivity and oceanic diffusion of heat. The model produces a pre-industrial climate that's dominated by volcanic eruptions, which is consistent with historic records and gives the authors a bit more confidence in their results. The results? To match the climate records with a confidence between 5 and 95 percent, the climate sensitivity values wound up being between 1.5 and 6.2 Kelvins, which is relatively good news, especially compared to some results that had placed it at over 9 Kelvins. It's likely to get hot in the coming century, but perhaps not catastrophically so.

The same Nature issue also includes data on something that might wind up being yet another wildcard that may result in sudden shifts in climate. We previously covered how the release of massive amounts of fresh water from glacial lakes could result in major disruption in ocean currents and, ultimately, global climate. You'd be forgiven for thinking that there are no major glacial lakes that pose such a risk today, but they're there: under the ice in Antarctica. The new report tracks how water can shift among the lakes in sudden surges that transfer over a cubic kilometer of water and cause deformations of the overlying ice. It's noted that, given the pressure on the lakes from the overlying ice, their ability to transfer water within a network presents the risk that, should part of that network open to the ocean, a catastrophic draining of the system could dump massive amounts of fresh water into the ocean, with potentially significant consequences.